Drivers: hv: vmbus: Implement per-CPU mapping of relid to channel

Currently the mapping of the relID to channel is done under the protection of a
single spin lock. Starting with ws2012, each channel is bound to a specific VCPU
in the guest. Use this binding to eliminate the spin lock by setting up
per-cpu state for mapping relId to the channel.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 70 insertions, 2 deletions

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 6f7fdd9a7e77..6c8b032cacba 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -149,6 +149,7 @@ static struct vmbus_channel *alloc_channel(void)
         spin_lock_init(&channel->sc_lock);
 
         INIT_LIST_HEAD(&channel->sc_list);
+        INIT_LIST_HEAD(&channel->percpu_list);
 
         channel->controlwq = create_workqueue("hv_vmbus_ctl");
         if (!channel->controlwq) {
@@ -188,7 +189,20 @@ static void free_channel(struct vmbus_channel *channel)
         queue_work(vmbus_connection.work_queue, &channel->work);
 }
 
+static void percpu_channel_enq(void *arg)
+{
+        struct vmbus_channel *channel = arg;
+        int cpu = smp_processor_id();
+
+        list_add_tail(&channel->percpu_list, &hv_context.percpu_list[cpu]);
+}
 
+static void percpu_channel_deq(void *arg)
+{
+        struct vmbus_channel *channel = arg;
+
+        list_del(&channel->percpu_list);
+}
 
 /*
  * vmbus_process_rescind_offer -
@@ -210,6 +224,12 @@ static void vmbus_process_rescind_offer(struct work_struct *work)
         msg.header.msgtype = CHANNELMSG_RELID_RELEASED;
         vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released));
 
+        if (channel->target_cpu != smp_processor_id())
+                smp_call_function_single(channel->target_cpu,
+                                         percpu_channel_deq, channel, true);
+        else
+                percpu_channel_deq(channel);
+
         if (channel->primary_channel == NULL) {
                 spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
                 list_del(&channel->listentry);
@@ -245,6 +265,7 @@ static void vmbus_process_offer(struct work_struct *work)
                                                         work);
         struct vmbus_channel *channel;
         bool fnew = true;
+        bool enq = false;
         int ret;
         unsigned long flags;
 
@@ -264,12 +285,22 @@ static void vmbus_process_offer(struct work_struct *work)
                 }
         }
 
-        if (fnew)
+        if (fnew) {
                 list_add_tail(&newchannel->listentry,
                               &vmbus_connection.chn_list);
+                enq = true;
+        }
 
         spin_unlock_irqrestore(&vmbus_connection.channel_lock, flags);
 
+        if (enq) {
+                if (newchannel->target_cpu != smp_processor_id())
+                        smp_call_function_single(newchannel->target_cpu,
+                                                 percpu_channel_enq,
+                                                 newchannel, true);
+                else
+                        percpu_channel_enq(newchannel);
+        }
         if (!fnew) {
                 /*
                  * Check to see if this is a sub-channel.
@@ -282,6 +313,14 @@ static void vmbus_process_offer(struct work_struct *work)
                         spin_lock_irqsave(&channel->sc_lock, flags);
                         list_add_tail(&newchannel->sc_list, &channel->sc_list);
                         spin_unlock_irqrestore(&channel->sc_lock, flags);
+
+                        if (newchannel->target_cpu != smp_processor_id())
+                                smp_call_function_single(newchannel->target_cpu,
+                                                         percpu_channel_enq,
+                                                         newchannel, true);
+                        else
+                                percpu_channel_enq(newchannel);
+
                         newchannel->state = CHANNEL_OPEN_STATE;
                         if (channel->sc_creation_callback != NULL)
                                 channel->sc_creation_callback(newchannel);
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index df2363ea017f..7f10c151632a 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -234,6 +234,28 @@ cleanup:
         return ret;
 }
 
+/*
+ * Map the given relid to the corresponding channel based on the
+ * per-cpu list of channels that have been affinitized to this CPU.
+ * This will be used in the channel callback path as we can do this
+ * mapping in a lock-free fashion.
+ */
+static struct vmbus_channel *pcpu_relid2channel(u32 relid)
+{
+        struct vmbus_channel *channel;
+        struct vmbus_channel *found_channel  = NULL;
+        int cpu = smp_processor_id();
+        struct list_head *pcpu_head = &hv_context.percpu_list[cpu];
+
+        list_for_each_entry(channel, pcpu_head, percpu_list) {
+                if (channel->offermsg.child_relid == relid) {
+                        found_channel = channel;
+                        break;
+                }
+        }
+
+        return found_channel;
+}
 
 /*
  * relid2channel - Get the channel object given its
@@ -285,7 +307,7 @@ static void process_chn_event(u32 relid)
          * Find the channel based on this relid and invokes the
          * channel callback to process the event
          */
-        channel = relid2channel(relid);
+        channel = pcpu_relid2channel(relid);
 
         if (!channel) {
                 pr_err("channel not found for relid - %u\n", relid);
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index bcb49502c3bf..edfc8488cb03 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -383,6 +383,8 @@ void hv_synic_init(void *arg)
          */
         rdmsrl(HV_X64_MSR_VP_INDEX, vp_index);
         hv_context.vp_index[cpu] = (u32)vp_index;
+
+        INIT_LIST_HEAD(&hv_context.percpu_list[cpu]);
         return;
 }
 
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 860134da8039..18d1a8404cbc 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -510,6 +510,11 @@ struct hv_context {
          * basis.
          */
         struct tasklet_struct *event_dpc[NR_CPUS];
+        /*
+         * To optimize the mapping of relid to channel, maintain
+         * per-cpu list of the channels based on their CPU affinity.
+         */
+        struct list_head percpu_list[NR_CPUS];
 };
 
 extern struct hv_context hv_context;